1. Field of the Invention
The present invention relates to hydraulic brake systems for vehicles, for example, for aircraft wheel brakes. Such hydraulic brake systems have return or low pressure lines as part of the hydraulic brake system circuit. In brake systems of this type there are sometimes conditions which create high pressures in the return lines due, for example, to operation of various hydraulic devices other than the brakes with the same hydraulic system. These other hydraulic devices have return lines in communication with the brake system return lines. The brakes in these systems must be designed so that they will release completely when hydraulic pressure is reduced by the brake control valve. However, with high brake return pressures in the low pressure return lines of the system, correspondingly high forces are needed to completely release the brakes by means of brake return springs. For example, if the system return pressure can be expected to be as high as 200 pounds per square inch (PSI) and the brake pistons have an area of 10 square inches, 2000 pounds of spring force would be necessary to release the brakes. Consequently such a braking system would require very heavy brake return springs with increased vehicle weight and cost of manufacture.
2. Description of the Prior Art
Brake systems currently in use include anti-skid systems with anti-skid valves for releasing brake fluid pressure when wheels being braked reach or approach skid conditions. Thus, any brake fluid control system for such brake systems should take into account the need for such anti-skid systems and their associated valves and hydraulic lines.
In hydraulically operated vehicle brake systems, such as on an aircraft or the like, it can happen that one of the pressure lines is broken or a brake becomes defective and leaks. It is thus important that some type of safety arrangement be provided in the event of a failure of part of the brake system, lest the hydraulic fluid supply pressure be diminished and the total brake system, not to mention the other hydraulic devices served by the hydraulic system, becomes inoperable. The prior art suggests various fusing and checkvalve arrangements for preventing the loss of system pressure on the failure of a single part thereof.